Problem

Azure OpenAI endpoints require an api-version query parameter on every API request. When users configure this in base_url (e.g. https://resource.openai.azure.com/openai?api-version=2025-04-01-preview), the OpenAI Python SDK silently drops query parameters during URL construction, resulting in HTTP 404 errors.

This is the same class of issue as #4599 (Azure Anthropic), but affecting the OpenAI SDK path used by custom providers.

Root Cause

The OpenAI SDK stores base_url as an httpx.URL and joins API paths (e.g. /responses, /chat/completions) onto it. During this join, any query parameters in the original URL are discarded — Azure never receives api-version and returns 404.

Fix

Extract query parameters from base_url before passing it to the OpenAI SDK, and forward them via the SDK's default_query parameter. This ensures they are appended to every outgoing request.

Files changed:

• run_agent.py — main agent client creation
• agent/auxiliary_client.py — auxiliary client creation (added _extract_url_query_params() helper, applied to all custom endpoint paths)

Backward Compatibility

• URLs without query params → default_query is None, original behavior unchanged
• URLs with query params → params extracted and forwarded correctly
• No hardcoded values — works for any provider requiring query parameters, not just Azure

Example Configuration

model:
  default: gpt-5.4  # Azure deployment name
  provider: custom
  base_url: https://your-resource.openai.azure.com/openai?api-version=2025-04-01-preview
  api_key: your-azure-key
  api_mode: codex_responses

Test Plan

• Azure OpenAI endpoint with api-version in base_url returns successful responses
• Standard OpenAI / OpenRouter / other providers without query params work unchanged
• Custom endpoints with arbitrary query params preserve them in requests